FIG. 1 is a view showing a carriage arm assembly 10 of the related art, where the axis X1–X2 represents the longitudinal direction, the axis Y1–Y2 represents the width direction, and the axis Z1–Z2 represents the height direction. The carriage arm assembly 10 has a structure in which a signal relay member 30 is mounted on a sub-assembly 11.
First, an explanation is given to the sub-assembly 11. Generally, the sub-assembly 11 includes a carriage arm body 12, a head slider 13, a driving coil 14, a bearing member 15, and a head IC 16.
The carriage arm body 12 is made of metals, includes a cylindrical housing 12a, an arm portion 12b extending from the cylindrical housing 12a in the X1 direction, and a fork portion 12c extending from the cylindrical housing 12a in the X2 direction.
The head slider 13 includes a magnetic head 19 that is embedded in one end thereof by photolithography, and is installed in gimbals 17a of a suspension 17 on the X1 side. The other end of the suspension 17 on the X2 side is fixed at a spacer 18, and the spacer 18 is fixed at an end of the arm portion 12b. The suspension 17 has a handle 17a at the end of the suspension 17 on the X2 side; the handle 17a is on the Y2 side of the suspension 17, and is projecting in the Z1 direction. In the suspension 17, a wiring pattern 20 is formed between the gimbals 17a and the handle 17b. Terminals on the magnetic head 19 are electrically connected with terminals on one end of the wiring pattern 20. The other end of the wiring pattern 20 reaches the handle 17b, and functions as terminals 21. On the handle 17b, four terminals are arranged in a line. The terminals 21 are at positions at the same height as a long and narrow side surface 12b1 of the arm portion 12b. 
The driving coil 14 is roughly a square, being fixed on the fork portion 12c. The bearing member 15 is installed in the housing 12a. 
The head IC 16 is built on a flexible board 26, on which a wiring pattern and terminals 25 are formed. The flexible board 26 is bonded on a base metal plate 27.
The base metal plate 27 is screwed to a side surface of the housing 12a on the Y2 side. A U-shaped bending portion of the base metal plate 27 functions as a connector 28.
After the carriage arm assembly 10 is installed in the hard disk drive, the connector 28 is connected to a flexible cable connector extending from a printing board of the hard disk drive, and thereby, the head IC 16 is electrically connected to a hard disk controller on the printing board. Terminals 25 are at positions closer to the X1 side than the head IC 16, and arranged in a line at positions at the same height as the long and narrow side surface 12b1 of the arm portion 12b. So far, the structure of the sub-assembly 11 is described.
FIG. 2, FIG. 3 and FIG. 4 show the signal relay member 30.
The signal relay member 30 has a long and narrow shape in correspondence to the shape of the side surface 12b1 of the arm portion 12b, and a copper wiring pattern 32 and terminals 33 and 34 at ends of the wiring pattern 32 are formed on a polyimide flexible base 31 of the signal relay member 30. A polyimide flexible cover 35 is bonded on the flexible base 31 by using a polyamide adhesive agent 36 to cover the wiring pattern 32. A two-sided adhesive tape 37 with a protection sheet thereon is pasted on the flexible cover 35.
After the protection sheet is removed, as illustrated in FIG. 5, the signal relay member 30 is fixed up with the side surface 12b1 of the arm portion 12b of the sub-assembly 11, which is supported by an assembling fixture 40 with the bearing member 15 being supported by the assembling fixture 40, and as illustrated in FIG. 6, the signal relay member 30 is bonded to the side surface 12b1 by the two-sided adhesive tape 37, then is heated with solder, as illustrated in FIG. 7, so that the terminals 33 are bonded with the terminals 21, and the terminals 34 are bonded with the terminals 25. In this way, the carriage arm assembly 10 is manufactured.
The magnetic head 19 is electrically connected to the head IC 16 through the wiring pattern 20 and the signal relay member 30. The assembling fixture 40 is grounded to prevent static electricity.
The signal relay member 30 may become charged with static electricity if it is subjected to friction while being mounted. However, because the whole surface of the signal relay member 30 is made of polyimide, which is insulating, when being mounted, even when the signal relay member 30 is in contact with the metal arm portion 12b, the static electricity can hardly flow to the carriage arm body 12, and the signal relay member 30 sill possesses static electricity. When the terminals 33 are bonded to the terminals 21, the static electricity flows to the magnetic head 19 through the terminals 33, terminals 21, and the wiring pattern 32, and depending on the situation, the magnetic head 19 may be destroyed by the static electricity.
In addition, the mounting position of the signal relay member 30 on the side surface 12b1 of the arm portion 12b is not uniquely defined, thus bonding of the terminals 33 with the terminals 21 and bonding of the terminals 34 with the terminals 25 are troublesome, that is, operability is low.